Profiled strips extruded of polymeric materials are widely used in automobile body applications as molding pieces. Molding pieces such as body side moldings or wheel well moldings are used to protect a vehicle body from impact damage and to protect edges of sheet metal panels from corrosion. Most of these molding pieces are extruded of thermoplastic materials such as PVC (polyvinyl chloride), thermoplastic rubber, thermoplastic urethane, or other flexible polymeric materials. PVC is one of the most widely used materials for its low cost and good physical properties.
Molding pieces such as a body side molding may be extruded of a plastic material alone or extruded in an extrusion coating process where plastic material is extruded on a metal reinforcing substrate. In an extrusion coating process where plastic material is combined with a more rigid metal substrate, a cross-head extrusion technique is used. In cross-head extrusion, a continuous length of metal reinforcing substrate is pulled through an extrusion die at 90.degree. angle to the direction of the plastic flow while molten plastic material is being extruded onto the metal substrate. The metal reinforcing substrate is usually cleaned and dried through a multi-station process and formed by a series of metal roll formers prior to the entry into the extrusion die. However, such metal reinforcing substrate may also be in the form of a thin metal foil which does not require preforming.
In automobile body parts, the aesthetic appearance of the part is one of the most important criteria that must be satisfied. In the extrusion of vinyl or vinyl/metal substrate reinforced molding pieces, the quality of the appearance of the molding pieces obtained is dependent upon many variables. One of these variables is how well the ends of the molding pieces are finished.
Currently, the industry practice is to cut the continuous length extrudate into appropriate lengths in-line after cooling of the extrudate. Even though this is a relatively efficient process, the parts produced, particularly the shear cut ends, are crude and unfinished. The metal substrate running through the center of the extrusion is frequently exposed at both ends of the cut molding pieces which is aesthetically unacceptable.
It is, therefore, an object of the present invention to provide a method of extrusion shaping profiled strips of polymeric material with smooth finished ends.
It is another object of the present invention to produce extruded profiled strips of polymeric material that have substantially no exposed metal substrate in the ends.
It is a further object of the present invention to extrude profiled strips of polymeric material having smooth finished ends without using labor intensive secondary finishing steps.